High Density Storage of Ammonia

ABSTRACT

A solid ammonia storage and delivery material comprising an ammonia absorbing/desorbing solid material, said storage and delivery material having been compacted to a density above 50% of the theoretic skeleton density provides a solid ammonia storage material which is easy to produce and handle and has a very high density of stored ammonia which is readily released under controlled conditions even though the porosity of the material is very low, and which storage material is safe for storage and transport of ammonia without special safety measures.

BACKGROUND OF THE INVENTION

The present invention relates to safe and compact storage for storingammonia, a method for producing a compact storage for storing ammonia,systems comprising a compact storage for delivery of ammonia to ammoniaconsuming units and use

1. Field of the Invention

The present invention relates generally to the use of using solids forreversible storage of ammonia in solid form. In the solid form, ammoniacan be transported safely, efficiently and can be released by thermaldesorption and used in various applications such as fuel cells and incontrolled delivery in selective catalytic reduction of NO_(x) usingammonia as reducing agent.

Transporting ammonia as a pressurized liquid is hazardous if thecontainer bursts caused by an accident or if a valve or tube breaks. Inthe case of using a solid storage medium, the safety issues are muchless critical since a small amount of heat is required to release theammonia and the equilibrium pressure at room temperature can be—if aproper solid material is chosen—well below 1 bar.

The invention relates to the storing ammonia in solids for the purposeof ammonia storage, transport and delivery to stationary and mobileapplications such as catalytic removal of NO_(x) (selective catalyticreduction using ammonia).

The present invention is especially suitable as a source for providingammonia in selective catalytic reduction in exhaust gasses for reductionof emission from stationary and mobile combustion engines or powerplants fuelled by methanol, ethanol, hydrogen, methane, ethane or anyother synthetic fuel. Mobile combustion engines for which the inventionis suitable are may e.g. be automobiles, trucks, trains, ships or anyother motorised vehicle. The invention is particularly suitable for usein connection with reduction of NO_(x) in combustion gases fromautomobiles and trucks.

Stationary power plants for which the invention is suitable arepreferably power plants generating electricity.

Furthermore, the solid ammonia storage material can be used as energycarrier applied in the field of fuel cell technology. Ammonia can becatalytically decomposed into N₂ and H₂ for the use in PEM fuel cellsand alkaline fuel cells or directly as ammonia in SOFC's (Solis OxideFuel Cells) and alkaline fuel cells. With a high ammonia storagedensity, the energy required to desorb and decompose ammonia still makesit a well-suited candidate for indirect hydrogen storage.

The critical part of preparing a useful solid ammonia storage medium isto obtain sufficiently high ammonia content—in particular with respectto the amount of ammonia per unit volume of the storage medium. This canbe related to the demands from DOE (US Department of Energy) forhydrogen storage. Efficient ammonia storage can just as well beconsidered as an efficient hydrogen storage material due to the highhydrogen content in NH₃.

2. Description of the Related Art

In published international application No. WO 90/10491 is disclosedcontrol of volumetric expansion of e.g. ammonia complexes of saltsduring adsorption and desorption in order to maintain heat transfer andreaction rates. This is obtained by compression by means of an outerbarrier limiting the volumetric expansion during chemisorption.

Published US patent application No. US 2001/0053342 discloses a methodfor selective NOx reduction in oxygen-containing exhaust gases usingammonia and a reduction catalyst according to which gaseous ammonia ismade available by heating a solid storage medium in a container.

US 2001/0053342 is silent with respect to compacting of the solidstorage medium.

SUMMARY OF THE INVENTION

In a first aspect the invention relates to a solid ammonia storage anddelivery material comprising an ammonia absorbing/desorbing solidmaterial, said storage and delivery material having been compacted to adensity above 50% of the theoretic skeleton density.

In a second aspect the invention relates to a method for storing ammoniain a solid material comprising steps of:

a) providing and binding ammonia in a solid material capable of bindingammonia; and

b) compacting the ammonia-containing material into a dense, solidmaterial having a density above 50% of the theoretic skeleton density.

In a third aspect the invention relates to a system for delivery ofammonia to an ammonia consuming unit wherein the system comprises adischarge chamber for delivery of ammonia, said chamber comprising anammonia absorbing/desorbing solid material, said material having beencompacted to a density above 50% of the theoretic skeleton density,means for heating the storage, and means for conveying the deliveredammonia from the storage chamber to one or more ammonia consuming units.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is disclosed more in detail with reference to the drawingsin which

FIG. 1 schematically shows a device for compression of an ammoniadelivery material,

FIG. 2 schematically shows an embodiment of an ammonia delivery deviceof the invention,

FIG. 3 schematically shows another embodiment of an ammonia deliverydevice of the invention,

FIG. 4 schematically shows a system according to the invention fordelivery of ammonia to fuel cells,

FIG. 5 schematically shows another system according to the invention fordelivery of hydrogen to fuel cells,

FIG. 6 schematically shows a further embodiment of an ammonia deliverydevice of the invention,

FIG. 7 is a graphical representation of the formation of pores duringthe desorption of ammonia from MgCl₂, and

FIG. 8 shows photographs of a tablet of the invention before and afterrelease of ammonia.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to the compaction of a solid storagematerial containing absorbed or chemically coordinated ammonia. Inparticular, the present invention relates to the use of metal-amminesalts as solid storage media for ammonia. Ammonia can form an amminesalt by exposing an anhydrous metal salt, e.g. CaCl₂, SrCl₂ or MgCl₂, togaseous ammonia in a saturation unit. During the formation of themulti-coordinated metal ammine, e.g. Mg(NH₃)₆Cl₂, the lattice of thesalt crystal grains expands significantly and the initial grains of thesalt partly disintegrates and forms a brittle structure of fine powder,which can be difficult to handle. Consequently, there is a significantporosity of the material, which reduces the volumetric ammonia capacityby a factor of approximately 2-4. In the case of magnesium chloride, thehexa-coordinated ammine salt (Mg(NH₃)₆Cl₂) has a skeleton density of1.25 g/cm³. The mass fraction of ammonia in saturated metal ammine saltsis generally high. In the case of Mg(NH₃)₆Cl₂, 51.7% of the total massis ammonia. Using the skeleton density, the maximal (theoretical)ammonia capacity is approximately 0.65 g NH₃/cm³. However, theas-prepared Mg(NH₃)₆Cl₂ has a density of roughly 0.2-0.3 g/cm³ due to alarge internal porosity and thus a volumetric ammonia density of roughly0.1 to 0.15 g NH₃/cm³.

The present invention relates to a solid ammonia storage and deliverymaterial comprising an ammonia absorbing/desorbing solid material, saidstorage and delivery material having been compacted to a density above50% of the theoretic skeleton density.

When a metal ammine complex of a salt is compressed to such a highextent—i.e. to a tablet or a block with essentially no void—desorptionfrom such a compacted material would be expected to be extremely slow,mostly due to diffusion hindrance. In most such materials desorption ofammonia would involve solid phase diffusion which is known to be a slowprocess for virtually all materials. This has surprisingly been foundnot to be the case for the dense materials according to the presentinvention. It has been found that when ammonia desorbs, a progressingnano-porous structure is formed as the “reaction front” proceeds,leaving open paths for additional ammonia to leave the central parts ofthe body of storage material. This is in contrast to e.g. classicalheterogeneous catalysis where conversion of reactants is only possible,if reactants are able to diffuse into the catalyst pore structure andthe products are able to diffuse out of the catalyst pore structure.

According to the invention it has now been found that it is possible toobtain a solid ammonia storage material which is easy to produce andhandle and has a very high density of stored ammonia which is readilyreleased under controlled conditions even though the porosity of thematerial is very low, and which storage material is safe for storage andtransport of ammonia without special safety measures. By increasing theeffective density—close to the skeleton density—the storage methodbecomes a commercially competitive technology.

In a preferred embodiment the storage and delivery material has beencompacted to a density above 70% of the theoretic skeleton density, morepreferred to a density above 75% such as above 80% and most preferredabove 85% of the theoretic skeleton density.

The expression “skeleton density” is used in the present context todefine the density of an “ideal” single crystal with no internal void,which density is determined by the distance between the ions (latticeconstants) in the material and the masses of the involved atoms (theskeleton density is the density of the solid material without anyinternal porosity). In a polycrystalline material, i.e. a powder, thereal bulk density is easily 4-8 times lower due to the large voidbetween the individual crystal grains. It has been found that it ispossible to compact the ammonia-saturated material to a very highdensity—very close to the upper theoretical limit, which is set by thetheoretical crystal skeleton density.

According to the present invention, ammonia is absorbed in a solidammonia storage and delivery material which is then compacted under ahigh pressure of several tons/cm² to reach nearly the theoreticaldensity, whereafter desorption takes place essentially without counterpressure.

In a preferred embodiment of the invention the storage and deliverymaterial comprises ammonia adsorbed or chemically bonded or coordinatedas a chemical complex in the form of a solid material that has beencompressed into a block or tablet or a pellet of a desired shape.

Forming complexes and compacting according to the invention providessolids having a high volumetric density as opposed to “simple”absorption resulting in solids that are rather porous and, consequently,the volumetric ammonia density (moles NH₃/m³ or kg NH₃/m³) can as low as10-50% of the theoretical value due to the internal porosity in thesaturated material.

The term “tablets” is used in the present context to designate smallertablets, monoliths or larger blocks or solid bodies of any convenientshape such as a ring.

In accordance with the invention it is preferred that the solid materialis a salt that binds ammonia in the form of a chemical complex as suchsalts have proven special advantages as will explained below.

In a preferred embodiment of the invention the solid material is anionic salt of the general formula:

M_(a)(NH₃)_(n)X_(z),

wherein M is one or more cations selected from alkali metals such as Li,Na, K or Cs, alkaline earth metals such as Mg, Ca or Sr, aluminium andtransition metals such as V, Cr, Mn, Fe, Co, Ni, Cu or Zn orcombinations thereof such as NaAl, KAl, K₂Zn, CsCu or K₂Fe, X is one ormore anions selected from fluoride, chloride, bromide, iodide, nitrate,thiocyanate, sulphate, molybdate and phosphate ions, a is the number ofcations per salt molecule, z is the number of anions per salt molecule,and n is the coordination number of 2 to 12.

It is especially preferred that the solid material comprises at leastone salt in the form of at least one chloride or sulphide of at leastone alkaline earth metal as these compounds are relatively cheap andreadily absorbs and desorbs ammonia under controlled conditions. Thesematerials also have relatively low molecular masses and the resultingammonia density calculated as a mass fraction will be higher.

Especially preferred the solid materials are MgCl₂, CaCl₂ and SrCl₂ andmixtures thereof, especially MgCl₂ due to the especially advantageousproperties.

In accordance with a further embodiment of the invention the solidmaterial is mixed with a binder in order to enhance the mechanicalstability of the compacted solid or to facilitate the compactionprocedure itself. Suitable binders are inert fibres that do notadversely affect the absorption/desorption of ammonia, e.g. fibres fromSiO₂, which will provide cohesion to the structure on larger lengthscales than just the individual crystal grains of the compactedmaterial.

As opposed to a “fluffy” powder, the compacted material can easily behandled during transport and during and after the final application.

It has surprisingly been found that a powdered ammonia delivery materialof the present invention has a very low vapour pressure of ammonia atroom temperature may be compacted to a very high density using severaldifferent methods for shaping of the material into a desired form andstill be capable of delivery of ammonia at a sufficient rate to besuitable for use as a source of ammonia for a SCR reduction of NOx ine.g. automotive vehicles, boilers and furnaces. Such methods are e.g.pressing, extrusion, and injection moulding. In the case of pressing, apressure might be applied in several different ways in a manner knownper se. In one embodiment, the material is compressed to shapes likedense blocks or tablets by placing the saturated salt in agroove/dent/hole/pit in a metal block (e.g. in a cylindrical hole) andapplying pressure to compress the material using a piston.

The metal-ammine salts constitute a solid storage medium for ammonia,which represent a safe, practical and compact option for storage andtransportation of ammonia. As an example, a single-crystalline compoundof Mg(NH₃)₆Cl₂ has an ammonia density of 38 kmole NH₃/M³, whereas thatof liquid ammonia is only slightly higher (40 kmole NH₃/m³). Ammonia maybe released from the metal ammine salt by heating the salt totemperatures in the range from 10° C. to the melting point of the metalsalt ammine complex, preferably to a temperature from 30 to 700° C.,more preferred to a temperature from 100 to 500° C.

During release of ammonia the metal-ammine salt of the formulaM_(a)(NH₃)_(n)X_(z) wherein M, X, a, n, and z has the meaning statedabove, is gradually transformed into a salt of the formulaM_(a)(NH₃)_(m)X_(z) wherein 0≦m<n. When the desired amount of ammoniahas been released, the resulting salt of formula M_(a)(NH₃)_(m)X_(z) canusually be converted back into the salt of the formulaM_(a)(NH₃)_(n)X_(z) by treatment with a gas containing ammonia.

As an example, anhydrous MgCl₂ absorbs up to six moles of NH3 (GmelinsHandbuch, 1939; Liu, 2004) according to reactions 1 to 3:

MgCl₂(s)+NH₃(g)

Mg(NH₃)Cl₂(s)  (1)

Mg(NH₃)Cl₂(s)+NH₃(g)

Mg(NH₃)₂Cl₂(s)  (2)

Mg(NH₃)₂Cl₂(s)+4NH₃(g)

Mg(NH₃)₆Cl₂(s) (3)

Typical ammonia contents of the metal ammine complexes are in the rangeof 20-60 wt %, and preferred complexes comprise above 30 wt % ammonia,more preferred above 40 wt % ammonia. The inexpensive compoundMg(NH₃)₆Cl₂ contains 51.7 wt % ammonia. A similar inexpensive compoundbased on CaCl2, i.e. Ca(NH3)₈Cl₂ contains 55% by weight ammonia.

The present invention offers ammonia storage at significantly higherdensities (both on a volume and a weight basis) than both aqueousammonia and aqueous urea. For several metal ammine salts it is possibleto release all ammonia and then transform the resulting material backinto the original metal ammine salt in a large number of cycles.Additionally, the ammonia is directly delivered into the exhaust pipe asa gas, which is an advantage in itself—both for the simplicity of theflow control system and for an efficient mixing of reducing agent,ammonia, in the exhaust gas—but it also eliminates possible difficultiesrelated to blocking of the dosing system because of precipitation in theliquid-based system.

For many applications wherein ammonia-related safety is essential, thecompacted Mg(NH₃)₆Cl₂ complex offers a further advantage in that thevapour pressure of ammonia above a solid salt phase is below 0.1 bar atroom temperature, preferably below 0.01 bar and even as low as 0.002 barat room temperature and atmospheric pressure. In practice, thiseliminates any noxious effect of the ammonia as the release of ammoniais as low as or lower than the release from common cleaning materialscontaining ammonia.

For Mg(NH₃)₆Cl₂ the partial pressure of ammonia at room temperature is0.002 bar. Even though a partial pressure of ammonia of 0.002 bar atambient temperature in itself could cause health problems, the compactedmaterial according to the invention saturated with ammonia releasesammonia at a very slow rate at ambient temperature and an equilibriumpressure of 0.002 bar will only be obtained after a considerable span oftime, even if the material is placed in a very confined space. However,when raising the temperature e.g. in the delivery device, a quite quickdesorption of ammonia is observed as discussed above.

For mobile units, it is particularly useful to use an ammonia deliverydevice comprising a container containing the metal ammine complex assuch a container may easily be separated from mobile unit and replacedby a fresh at suitable intervals. In preferred embodiments, the metalammine containers are recycled and recharged with ammonia in a separaterecharging unit. In other preferred embodiments the material isre-saturated with ammonia in situ or on-board by connecting a source ofammonia (e.g. a large tank containing liquid ammonia) to the storagecontainer and thus exposing the ammonia-depleted salt in the containerto gaseous or liquid ammonia.

Due to the slow release of ammonia in open atmosphere at ambienttemperatures for the compressed materials of the present invention, thehandling of the materials does not necessarily require extensive safetyprecautions. Therefore, substitution of exhausted storage and deliverymaterial with fresh material does not necessarily require anencapsulation of the material facilitating the handling as compared tothe handling of the materials used in the methods of the state of theart.

In a second aspect the invention relates to a method for storing ammoniain a solid material comprising steps of:

a) providing and binding ammonia in a solid material capable of bindingammonia; and

b) compacting the ammonia-containing material into a dense, solidmaterial having a density above 50% of the theoretic skeleton density.

In accordance with the invention it is possible to form the dense solidmaterial into a desired shape during compaction or in a subsequentprocessing step.

In a preferred embodiment the present invention is related to thecompaction and shaping of the saturated ammonia storage and deliverymaterial.

Prior to compaction, the solid material suitably consists of a granularmaterial, a porous material, a crystalline material, an amorphousmaterial or a combination thereof.

The saturated solid, e.g. Mg(NH₃)₆Cl₂ can be compacted significantly byseveral different methods, which also includes shaping of the materialinto a desired form. Such methods include: pressing, extrusion andinjection moulding. In the case of pressing, a pressure might be appliedin several different ways. In one embodiment, the material is compressedto shapes like dense blocks or tablets by placing the saturated salt ina groove/dent/hole/pit in a metal block (e.g. in a cylindrical hole) andapplying pressure to compress the material using a piston pressedagainst the initially porous or powdery solid.

In a preferred embodiment of the invention the solid material iscompacted and shaped in a mould using mechanical pressure.

Compacting and shaping of the solid material may suitably be carried outin a manner known per se such as injection moulding, extrusion ormonolith preparation.

The compacted solid ammonia storage material can be prepared e.g. in theform of cylinders, rods, cubes, rectangular shaped blocks or othershapes having overall dimensions suitable to the desired ammoniaconsumption in the ammonia consuming unit. For some applicationsrequiring only a small amount of ammonia, the weight of the compactedstorage unit may be below 10 g. In other applications requiring largeamounts of ammonia, the rods/blocks/cylinders (or other shapes) may evenbe above 100 kg in size. The corresponding volume of the units may alsovary from below 1 cm³ to above 1000 litres. Examples of different sizesand shapes (but mot limited to those) are:

-   -   1. tablets with a diameter of 13 millimetres and a height of 10        millimetres,    -   2. ring-shaped units having dimensions of the magnitude of        centimetres such as an outer diameter of 52 millimetres, a hole        of a diameter of 27 millimetres and a height of 13 millimetres,        or    -   3. cubes having a length of about 10 centimetres and preferably        having rounded edges.

The more regular shapes bodies are preferred when several pieces ofcompacted materials are to be placed in a common container as the spacemay then be utilized more efficiently than e.g. packing of spheres.

In one embodiment of the method of the invention the solid materialbinds ammonia by absorption, and ammonia is preferably bound in solidmaterial in the form of a chemical complex.

It is preferred to saturate the solid material completely with ammoniato reach its maximum capacity. On the other hand it may be acceptablefor economical reasons not to saturate the material completely in caseswhere a full saturation of larger units requires a very long saturationtime.

In one embodiment the invention relates to a method of producing a solidammonia storage and delivery material comprising an ammonia absorbingsalt, wherein the ammonia absorbing salt is an ionic salt of the generalformula:

M_(a)(NH₃)_(n)X_(z),

wherein M is one or more cations selected from alkali metals such as Li,Na, K or Cs, alkaline earth metals such as Mg, Ca or Sr, Al andtransition metals such as V, Cr, Mn, Fe, Co, Ni, Cu or Zn orcombinations thereof such as NaAl, KAl, K₂Zn, CsCu or K₂Fe, X is one ormore anions selected from fluoride, chloride, bromide, iodide, nitrate,thiocyanate, sulphate, molybdate and phosphate ions, a is the number ofcations per salt molecule, z is the number of anions per salt molecule,and n is the coordination number of 2 to 12, said method comprising thesteps of

1) providing the solid salt,

2) saturating the salt with ammonia, and

3) compressing the ammonia salt complex.

The expression “saturated” is used in the present context to define astate in which the material cannot take up more ammonia according to theabsorption reactions or the capacity of the solid in general. As anexample, for MgCl₂, the material is fully saturated when six NH₃molecules are coordinated around each MgCl₂-unit, i.e. Mg(NH₃)₆Cl₂.CaCl₂ can take up 8 molecules of ammonia per unit CaCl₂.

A powdery ammonia saturated material may be prepared by exposing the drysalt to gaseous ammonia in a manner known per se. The ammonia saturateddelivery material as prepared is powdery and rather “fluffy” anddifficult to handle or transport and may be—during transport oruse—transformed into small particle fragments thereby potentiallyblocking the dosing system of a device or give rise to hazardous dustinto the environment. Furthermore, the powder has a low bulk density.

In a preferred embodiment of the method of the invention, the ammoniasalt complex is compressed to a density of 1.0 to 1.3 g/cm³, morepreferred to a density of 1.1 to 1.3 g/cm³

In a preferred embodiment of the invention the solid material comprisesat least one salt in the form of at least one chloride or sulphide of atleast one alkaline earth metal. Such materials have proven very suitablefor the purpose of the present invention, are readily available and arerelatively safe to use. The solid material is preferably MgCl₂, CaCl₂ orSrCl₂ or mixtures thereof.

In a further embodiment of the invention the method further comprisesthe step of mixing the solid material with a binder before compactingthe solid material in order to enhance the mechanical stability of thecompacted solid or to facilitate the compaction procedure itself and toprovide cohesion to the structure.

In one embodiment of the invention the method further comprises thesteps of

c) placing the compacted ammonia-containing material in a closed chamberprovided with means for conveying ammonia from the chamber to one ormore ammonia consuming units, and

d) heating the chamber for releasing ammonia.

It is preferred that the ammonia is conveyed by normal pressure-drivenflow through connection tubes to the ammonia-consuming units and whereinthe pressure is controlled directly by heating the chamber containingthe compact ammonia storage material.

In a further embodiment of the invention, the method further comprisesthe step

e) providing and binding ammonia in the solid material depleted ofammonia for reusing the solid material.

Thus, in one embodiment a method of the invention comprises the steps of

i) providing a container with compacted ammonia storage material

ii) releasing the ammonia form the storage container to an ammoniaconsuming unit by heating the container, and

iii) re-saturating the storage container with ammonia by re-absorbingammonia into the material by providing gaseous or liquid ammonia througha connection to the storage container.

It is preferred to carry out the re-saturation with ammonia by providingliquid ammonia to the storage material or storage container, after ithas been depleted for ammonia. Using liquid ammonia accelerates there-saturation because the endothermic evaporation of liquid ammoniatakes up part of the heat evolved when ammonia is absorbed in thedepleted material. Furthermore, the necessary capacity of heat exchangefor carrying out fast resaturation in larger units is minimised whenheat evolvement from the resaturation process is utilized forevaporation of the liquid ammonia. This renders it possible tore-saturate in situ.

In a third aspect the invention relates to a system for delivery ofammonia to an ammonia consuming unit wherein the system comprises adischarge chamber for delivery of ammonia, said chamber comprising anammonia absorbing/desorbing solid material, means for heating thestorage material, and means for conveying the delivered ammonia from thestorage chamber to one or more ammonia consuming units.

The ammonia consuming unit may suitably be a system wherein ammonia isused for catalytic removal of NO_(x). In a further embodiment theammonia consuming unit is an internal combustion engine fuelled byammonia, a fuel cell capable of using ammonia as a fuel. Still further,the ammonia consuming unit may a catalytic reactor decomposing theammonia into hydrogen and nitrogen, and such unit suitably comprisesmeans for conveying the hydrogen to one or more fuel cells usinghydrogen as fuel.

In one embodiment of the system of the invention the system comprises afeeding system for continuous feeding of solid ammonia storage anddelivery material into the discharge chamber wherein ammonia is releasedby thermal desorption.

In a still further embodiment of the invention the system furthercomprises:—a feeding system comprising a number of compartments whereeach compartment comprises one or more unit(s) of solid ammonia storageand delivery material, which feeding system is adapted to introducingthe units sequentially into the discharge chamber wherein ammonia isreleased by thermal desorption.

In another embodiment of the invention the system comprises a feedingsystem in which the total amount of ammonia storage material is dividedinto minor parts or sections being heated separately, thus avoiding theneed of heating the entire mass of storage material simultaneously inorder to release ammonia and to introduce new units of ammonia storagematerial when the ammonia content of one unit is discharged.

The system preferably further comprised means for supplying ammonia tothe storage chamber for re-saturate the material in situ.

A system of the invention typically comprises a container comprising anammonia absorbing salt, said container being provided with one or moreclosable outlet opening(s) connected to a pipe and further beingprovided with means for heating the container and the ammonia absorbingsalt for release of gaseous ammonia as a source for ammonia.

The closable outlet opening(s) may be in the form of one or morevalve(s).

Heating means may be in the form of an electrical resistive heatingdevice.

The heating means may alternatively be provided as heat produced bychemical reactions or as heat from hot exhaust gas from a combustionprocess.

A metal ammine salt complex for delivery of ammonia is normally heatedto temperatures in the range from 10° C. to the melting point of themetal salt ammine complex, preferably to a temperature from 30 to 700°C., more preferred to a temperature from 100 to 500° C.

In a preferred embodiment of the invention the release rate of ammoniais controlled by accurate control of the heating of the container andthe ammonia absorbing salt for release of gaseous ammonia. The releaseof ammonia is preferably further controlled by reduction valves, flowcontrollers or similar equipment or units. The release may be furthercontrolled by introducing a buffer volume between the storage containerand the ammonia consuming unit in order to be able to compensate for arapidly fluctuating dosing of ammonia to the ammonia consuming unit. Therelease of ammonia from a container is preferably controlled byinteraction with an electronic engine control system for delivery of anoptimum amount of ammonia in a specific ratio (e.g. NH₃:NOx=1:1) of thechanging emission of NOx from an engine.

In a further aspect the invention relates to a device for providingammonia for a selective catalytic reduction of NO_(x) in anoxygen-containing exhaust gas of a combustion engine or combustionprocess by using gaseous ammonia and a reduction catalyst, the devicecomprising:

-   -   a container for containing a compacted solid storage material;    -   means for heating the container;    -   means for introducing gaseous ammonia from the container into an        exhaust line before the reduction catalyst;    -   means for controlling the amount of ammonia introduced into the        exhaust line, depending on the operating conditions of the        engine.

In a still further aspect the invention relates to a method of producinga solid ammonia storage and delivery material comprising an ammoniaabsorbing salt, said method comprising the steps of

-   -   1) providing the solid salt,    -   2) saturating the salt with ammonia, and    -   3) compressing the ammonia salt complex to a density above 50%        of the theoretic skeleton density.

The compacted ammonia storage solid is particularly useful forapplication such as:

-   -   Releasing ammonia into a solid oxide fuel cell for generation of        electrical energy    -   Releasing ammonia into a catalytic decomposition unit        (2NH₃→3H₂+N₂) with an optional absorption of remaining NH₃ and        feeding the generated hydrogen into a hydrogen based fuel cell,        e.g. a PEM fuel cell, an alkaline fuel cell, a phosphoric acid        fuel cell or a molten carbonate fuel cell.    -   A controlled release of ammonia—in some cases directly following        a dynamic NO_(x) transient—in order to use ammonia as a reducing        agent in selective catalytic removal of NO_(x) in exhaust gasses        from combustion engines.    -   In preferred embodiments the invention relates to

1) A power generating device comprising:

-   -   a container for containing a compacted solid storage material;    -   means for heating the container;    -   an electrochemical cell for converting ammonia into electrical        power;    -   means for introducing gaseous ammonia into the electrochemical        cell, and

2) A power generating device comprising:

-   -   a container for containing a compacted solid storage material;    -   means for heating the container;    -   a decomposing catalyst for decomposing the desorbed ammonia into        hydrogen and nitrogen;    -   means for introducing ammonia into the decomposing catalyst;    -   an electrochemical cell for converting hydrogen into electrical        power;    -   means for introducing gaseous hydrogen into the electrochemical        cell.

In a still further aspect the invention relates to the use of a solidammonia storage and delivery material comprising an ammoniaabsorbing/desorbing solid material, said storage and delivery materialhaving been compacted to a density above 50% of the theoretic skeletondensity as a source of ammonia in one or more ammonia consuming units.

In an embodiment the invention relates to the use of a solid ammoniastorage and delivery material comprising an ammonia absorbing/desorbingsolid material, said storage and delivery material having been compactedto a density above 50% of the theoretic skeleton density as a source ofammonia as the reducing agent in selective catalytic reduction (SCR) ofNO_(x) in exhaust gases from combustion processes.

In a preferred embodiment of the invention the solid material is anionic salt of the general formula:

M_(a)(NH₃)_(n)X_(z),

wherein M is one or more cations selected from alkali metals such as Li,Na, K or Cs, alkaline earth metals such as Mg, Ca or Sr, Al andtransition metals such as V, Cr, Mn, Fe, Co, Ni, Cu or Zn orcombinations thereof such as NaAl, KAl, K₂Zn, CsCu or K₂Fe, X is one ormore anions selected from fluoride, chloride, bromide, iodide, nitrate,thiocyanate, sulphate, molybdate and phosphate ions, a is the number ofcations per salt molecule, z is the number of anions per salt molecule,and n is the coordination number of 2 to 12. In a preferred embodimentfor SCR M is Mg.

In a preferred embodiment of the invention an ammonia delivery devicecomprising a container comprising an ammonia absorbing salt, wherein theammonia absorbing salt is an ionic salt of the general formula:

M_(a)(NH₃)_(n)X_(z),

wherein M is one or more cations selected from alkali metals such as Li,Na, K or Cs, alkaline earth metals such as Mg, Ca or Sr, aluminium andtransition metals such as V, Cr, Mn, Fe, Co, Ni, Cu or Zn orcombinations thereof such as NaAl, KAl, K₂Zn, CsCu or K₂Fe, X is one ormore anions selected from fluoride, chloride, bromide, iodide, nitrate,thiocyanate, sulphate, molybdate and phosphate ions, a is the number ofcations per salt molecule, z is the number of anions per salt molecule,and n is the coordination number of 2 to 12, said container beingprovided with one or more closable outlet opening(s) connected to a pipeand further being provided with means for heating the container and theammonia absorbing salt for release of gaseous ammonia is used as asource for ammonia in selective catalytic reduction of NO_(x) in exhaustgases from combustion processes.

In a preferred embodiment the invention relates to the use of a solidammonia storage and delivery material comprising a complex ammoniaabsorbing/desorbing solid material, said storage and delivery materialhaving been compacted to a density above 50% of the theoretic skeletondensity in connection with a PEM fuel cell, wherein the ammonia storagematerial has an ammonia pressure in the range of 0.1-15 bar between roomtemperature and the operating temperature of a fuel cell. In oneembodiment the complex solid ammonia storage and delivery material isCaCl₂, SrCl₂ or a mixture thereof. Such solid ammonia storage anddelivery material has a suitable supply-pressure of ammonia attemperatures obtainable when using waste heat from a conventionalPEM-fuel cell or alkaline fuel cells as a source of heat which reducesor eliminates the need of an external source of heat for the desorptionof ammonia.

In the explanation of the present invention the term “absorb” has beenused to designate the binding of ammonia to a solid material. This isnot considered as a limitation of the invention to the physicalabsorption to the extent that adsorption to the surface of a solidmaterial will provide the same option of desorbing the material in acontrolled manner using heat.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is now explained more in detail with reference to thedrawings showing preferred embodiments of the invention.

Preparation of Ammonia Saturated MgCl₂ Powder.

The ammonia carrier, Mg(NH₃)₆Cl₂, was prepared by placing a batch ofMgCl₂ powder for several days in a glove-bag containing ammonia gas atatmospheric pressure. The degree of saturation was checked bytemperature programmed desorption (TPD) and verified to be near 100% ofthe theoretical amount. The absorption/desorption was found to be fullyreversible.

The rate of absorption is dramatically increased at higher NH₃ pressures(minutes rather than days) (Touzain and Moundamga-Iniamy, 1994).

FIG. 1 schematically shows a device according to the present inventionfor compression of the solid ammonia storage medium. In this embodiment,the solid ammonia storage medium is compressed in a chamber by applyingmechanical force to a piston acting on the porous storage medium. Whenthe piston is removed, the storage medium is in the shape of a tablet,and has a density above 80% of the theoretical crystal density.

EXAMPLE 1 Compression of Solid Ammonia Storage Medium Into Tablets

FIG. 1 schematically shows a device according to one embodiment of theinvention for compression of 1 gram of the solid ammonia deliverymaterial for the preparation of cylindrical tablets (dimensions: 13 mmin diameter; 10 mm high). In this embodiment, the solid ammonia deliverymaterial was compressed in a chamber by applying a pressure of 2-4tons/cm² using a piston compressing the powdered saturated storagematerial. The chamber and the piston were made from stainless steel.When the piston was removed, the delivery material was in the desiredshape of e.g. a tablet, a cylinder or a rod, and had a density above 80%of the theoretical crystal density.

The tablets have densities in the range of 1.1-1.2 g/cm³, which isroughly an increase in effective density of the as-prepared powder by afactor of 4. The resulting tablet or block is compact, easy-to-handleand represents a safe ammonia storage material.

The structure of the densified storage tablet was verified by recordingan XRD spectrum of the hexa-coordinated ammine salt after tabletpressing. In addition, the tablet was placed in a testing unit, whichslowly degasses the ammonia by thermal desorption. The total ammoniacontent in terms of mass fraction was verified to be above 99% of thetheoretical amount. Thus the invention provides the possibility ofmaking an ammonia storage material with an ammonia density above 0.6 gNH₃/cm³. For use as hydrogen storage, the hydrogen capacity is wellabove 6 % w/w. For the compacted Mg(NH₃)₆Cl₂, the hydrogen density is9.1% w/w and with the obtained solid density of the material thehydrogen density is 0.1-0.11 g H₂/cm³. The demonstrated density of atleast 0.6 grams NH₃/cm³ is above 90% of the volumetric density of liquidammonia stores under a pressure (8 bar) at room temperature.

FIG. 2 schematically shows an embodiment of an ammonia delivery deviceof the invention for desorption of the compressed delivery material. Inthis embodiment, one or more tablets of solid ammonia delivery material1 are placed in a container 2, which can be heated by a heating device3. Desorbed ammonia leaves the container through a nozzle 4. Heat forthe heating device 3 may be provided by e.g. resistive electric heatingor chemical reactions. Such chemical reactions could be generated e.g.by combustion of a part of the released ammonia or hydrogen produced byreforming of the released ammonia into hydrogen and nitrogen. If thedelivery device is used in connection with SCR of NOx in exhaust gases,waste heat from the engine producing the gases can also be applied.

The degassing of ammonia from the compacted storage medium can becarried of in a sequential manner as follows:

-   -   1. The desired total mass of saturated ammonia material is not        pressed into a single block but compressed into a number of        smaller units.    -   2. Each unit can be fed one at the time to a degassing unit        using heat (e.g. electrical or a heat exchanger) as degassing        method.    -   3. When one storage material unit is degassed, a new unit is fed        to the degassing chamber thus replacing the ammonia-depleted        unit.

Such a system has a significant advantage since only a minor fraction ofthe total mass has to be heated in order to release the continuous needfor ammonia down-stream in the process.

FIG. 3 schematically shows a preferred embodiment where only a part ofthe stored solid ammonia storage medium 1 is heated at a time. The solidstorage material is stored in compressed form, and introduced into a hotchamber 2 one at the time at intervals corresponding to the requirementfor gaseous ammonia. The hot chamber is heated by a heating device 3operated after the same principles as described for FIG. 2. Gaseousammonia leaves the hot chamber through a nozzle 4, and when all ammoniais desorbed from a tablet of solid ammonia storage material 5, it isdiscarded into a separate container 6.

In a similar type of embodiment, the entire storage material isseparated into a number of compartments each having their own heatingsource so that it is possible to have complete desorption of a givenfraction of the material without using any moving parts to replacesaturated/unsaturated salt e.g. on-board the vehicle during use.

FIG. 4 describes schematically an embodiment of a system according tothe invention, wherein ammonia is desorbed from the compacted solidstorage medium 1 and led directly into a power generating unit in theform of an ammonia fuelled fuel cell 11. In a preferred embodiment ofthis system according to the present invention the power generating unitis be a fuel cell of the SOFC type or an alkaline type fuel cell.

In FIG. 5 another embodiment of a system according to the presentinvention is described, wherein a compacted ammonia storage medium 1 isheated in a container 2 by a heating device 3. Desorption takes place inthe same way as described in connection with FIGS. 2 and 3. Afterleaving the container 2 through the pipe 4 the ammonia enters acatalytic reactor 7 wherein it is decomposed to hydrogen and nitrogen.Any residual ammonia may be removed in an optional purification unit 8.The resulting hydrogen and nitrogen are rare then fed through pipe 9into an electrochemical power generating device in the form of ahydrogen fuelled fuel cell 10. In a preferred embodiment the fuel cellis a fuel cell of the PEM or alkaline type.

FIG. 6 schematically shows a further embodiment of an ammonia deliverydevice of the invention which comprises a number of individualcontainers (2) (Container 1,2, . . . , N) each comprising an ammoniastorage and delivery material (1) according to the invention andindividual sources of heat (Heat 1, Heat 2, . . . , Heat N) for heatingthe individual containers sequentially and individual valves for openingthe outlet (4) of the container from which ammonia is released.

EXAMPLE 2 Compression of Solid Ammonia Storage Medium Into Rings

In another embodiment of the invention rings or larger blocks of morecomplicated shapes of the storage material may be produced. In thisexample rings having an outer diameter of 52 millimetres and a centralhole having a diameter of 27 millimetres were made using the proceduredescribed in Example 1 using corresponding moulds made from stainlesssteel. 20 grams of the solid ammonia delivery material were compressedfor the preparation of rings (dimensions: outer diameter of 52millimetres, a central hole having a diameter of 27 millimetres andthickness (height) 13 millimetres). In this embodiment, the solidammonia delivery material was compressed in a chamber by applying apressure of 25 tons (about 1.57 tons/cm²) using a piston compressing thepowdered saturated storage material in a compression ratio of about 6.3.When the piston was removed, the delivery material was in the desiredshape of a ring, and had a density above 80% of the theoretical crystaldensity.

FIG. 7 is a graphical representation showing the formation of poresduring desorption of ammonia from the compacted and saturatedMg(NH₃)₆Cl₂ before and after the transformation into a porous block ofMgCl₂. The pore size distribution was measured using a MicromeriticsASAP 2010 apparatus during desorption as a function of the degree ofrelease, and it appears that although nearly no porosity was presentinitially, the size of the pores increase with increasing degree ofdesorption facilitating the further desorption of ammonia. This enablesthe release of ammonia from large blocks or rods or similar shapes ofthe saturated ammonia storage material even though initially there isessentially no pore system in the material.

FIG. 8 shows a photograph of a tablet of Mg(NH₃)₆Cl₂, which is (left)fully saturated with ammonia and a fractured surface thereof. It can beseen that the overall structure of the tablet is retained afterdesorption (right) but the internally, the tablet has become porous inaccordance with to the pore volume measurements presented in FIG. 7. Inother words, the dense, saturated tablet has been transformed into aporous “sponge” of depleted salt.

In another experiment a quite low bed-density of the delivery materialwas obtained when Mg(NH₃)₆Cl₂ was compacted manually (331 kg/m³ whencompacted gently by hand) as compared to the density of MgCl₂ andMg(NH₃)₆Cl₂ compacted in accordance with the invention (1252 kg/m³, cf.the below table).

TABLE Mass density Molar volume Salt kg/m³ cm³/mole Source MgCl₂ 232540.86 CRC Handbook 2004 Mg(NH₃)₆Cl₂ 1252 157.4 Gmelins Handbook 1939

A low density means that the entire storage system would require morespace. This problem was in this example solved by compressingMg(NH₃)₆Cl₂ into solid rods having a density of 1219 kg/m³(97% of thesolid density) as disclosed in Example 1. TPD experiments confirmed thatit was possible to desorp all ammonia from this tablet, thus increasingthe potential storage capacity by a factor of 3.7 (on a molar basis) toapproximately 93% of the volumetric ammonia storage capacity of liquidammonia. A nearly quantitative desorption of ammonia from the densematerial was possible because the front of desorption leaves behind aporous layer of anhydrous MgCl₂. This automatically generates therequired pore system needed for mass-transfer through the structure.This is considered an ideal combination of a) an initially very compactstructure having almost no void and being easy to handle, b) a highcapacity for containing and delivering ammonia, c) a low externalsurface area, and d) a high degree of safety.

1-40. (canceled)
 41. A solid ammonia storage and delivery materialcomprising an ammonia absorbing/desorbing solid material, said storageand delivery material having been compacted to a density above 50% ofthe theoretic skeleton density.
 42. A material according to claim 41,said storage and delivery material having been compacted to a densityabove 75% of the theoretic skeleton density.
 43. A material according toclaim 42, said storage and delivery material having been compacted to adensity above 85% of the theoretic skeleton density.
 44. A materialaccording to claim 41 comprising ammonia absorbed or chemically bondedor coordinated as a chemical complex in the form of a solid materialthat has been compressed into a block or tablet or a pellet of a desiredshape.
 45. A material according to claim 41, wherein the solid materialis a chemical complex in the form of an ionic salt of the generalformula:M_(a)(NH₃)_(n)X_(z), wherein M is one or more cations selected fromalkali metals, alkaline earth metals, aluminium and transition metals orcombinations thereof, X is one or more anions selected from fluoride,chloride, bromide, iodide, nitrate, thiocyanate, sulphate, molybdate andphosphate ions, a is the number of cations per salt molecule, z is thenumber of anions per salt molecule, and n is the coordination number of2 to
 12. 46. A material according to claim 45, wherein the alkali metalsare selected Li, Na, K and Cs, the alkaline earth metals are selectedfrom Mg, Ca or Sr, and the combinations are selected from NaAl, KAl,K₂Zn, CsCu or K₂Fe.
 47. A material according to claim 45, wherein thesolid material comprises at least one salt in the form of at least onechloride or sulphide of at least one alkaline earth metal.
 48. Amaterial according to claim 47, wherein the solid material is MgCl₂,CaCl₂ or SrCl₂ or mixtures thereof.
 49. A material according to claim41, wherein the solid material is mixed with a binder.
 50. A method forstoring ammonia in a solid material comprising steps of: a) providingand binding ammonia in a solid material capable of binding ammonia; andb) compacting the ammonia-containing material into a dense, solidmaterial having a density above 50% of the theoretic skeleton density.51. A method according to claim 50, wherein the solid material to becompacted consists of a granular material, a porous material, apolycrystalline material, an amorphous material or a combinationthereof.
 52. A method according to claim 50, wherein the solid materialis compacted and shaped in a mould using mechanical pressure.
 53. Amethod according to claim 50, wherein the solid material is compactedand shaped using injection moulding, extrusion or monolith preparation.54. A method according to claim 50, wherein the solid material bindsammonia by adsorption.
 55. A method according to claim 54, wherein theammonia is bound in solid material in the form of a chemical complex.56. A method according to claim 50, wherein the solid material issaturated with ammonia.
 57. A method according to claim 50, wherein thesolid material contains at least one salt of the general formulaM_(a)(NH₃)_(n)X_(z), wherein M is one or more cations selected fromalkali metals, alkaline earth metals, aluminium and transition metals orcombinations thereof, X is one or more anions selected from fluoride,chloride, bromide, iodide, nitrate, thiocyanate, sulphate, molybdate andphosphate ions, a is the number of cations per salt molecule, z is thenumber of anions per salt molecule, and n is the coordination number of2 to
 12. 58. A method according to claim 57, wherein the alkali metalsare selected from Li, Na, K and Cs, the alkaline earth metals areselected from Mg, Ca or Sr, the transition metals are selected from V,Cr, Mn, Fe, Co, Ni, Cu and Zn, and the combinations thereof are selectedfrom NaAl, KAl, K₂Zn, CsCu or K₂Fe.
 59. A method of claim 58 producing asolid ammonia storage material comprising the steps of 1) providing thesolid salt, 2) saturating the salt with ammonia forming a chemicalcomplex, and 3) compacting the ammonia-saturated salt complex.
 60. Amethod according to claims 57, wherein the solid material comprises atleast one salt in the form of at least one chloride or sulphide of atleast one alkaline earth metal.
 61. A method as claimed in claim 60,wherein the solid material is MgCl₂, CaCl₂or SrCl₂ or mixtures thereof.62. A method according to claim 50 further comprising a step mixing thesolid material with a binder before compacting the solid material.
 63. Amethod as claimed in claim 50 further comprising the step of c) placingthe compacted ammonia-containing material in a closed chamber providedwith means for conveying ammonia from the chamber to one or more ammoniaconsuming units and means for heating the material in the chamber, andd) heating the chamber for releasing ammonia.
 64. A method as claimed inclaim 63, wherein the ammonia is conveyed by normal pressure-driven flowthrough connection tubes to the ammonia-consuming units and wherein thesupply pressure is controlled by heating the chamber containing thecompacted ammonia storage material.
 65. A method as claimed in claim 63further comprising the step e) providing and binding ammonia in thesolid material after it has been depleted of ammonia.
 66. A method asclaimed in claim 65 comprising the steps of i) providing a containerwith compacted ammonia storage material, ii) releasing the ammonia formthe storage container to an ammonia consuming unit by heating thecontainer, and iii) re-saturating the storage container with ammonia byre-absorbing ammonia into the material by providing gaseous or liquidammonia through a connection to the storage container.
 67. A system fordelivery of ammonia to an ammonia consuming unit wherein the systemcomprises a discharge chamber for delivery of ammonia, said chambercomprising a compacted ammonia absorbing/desorbing solid material, meansfor heating the storage, and means for conveying the delivered ammoniafrom the storage chamber to one or more ammonia consuming units.
 68. Asystem according to claim 67, wherein the ammonia consuming unit is asystem wherein ammonia is used for catalytic removal of NO_(x).
 69. Asystem according to claim 68, wherein the catalytic removal of NO_(x) isa selective catalytic reduction of NO_(x) in an oxygen-containingexhaust gas of a combustion engine or a combustion process.
 70. A systemaccording to claim 67, wherein the ammonia consuming unit is an internalcombustion engine fuelled by ammonia.
 71. A system according to claim67, wherein the ammonia consuming unit is a fuel cell capable of usingammonia as a fuel.
 72. A system according to claim 67, wherein theammonia consuming unit is a catalytic reactor decomposing the ammoniainto hydrogen and nitrogen.
 73. A system according to claim 72 furthercomprising means for conveying the hydrogen to one or more fuel cellsusing hydrogen as fuel.
 74. A system according to claim 67 furthercomprising a feeding system for continuous feeding of solid ammoniastorage and delivery material into the discharge chamber wherein ammoniais released by thermal desorption.
 75. A system according to claim 67further comprising: a feeding system comprising a number of compartmentswhere each compartment comprises one or more unit(s) of compacted solidammonia storage and delivery material, which feeding system is adaptedto releasing ammonia from the units sequentially by thermal desorption.76. A system according to claim 67 further comprising means forsupplying ammonia to the storage chamber.